/**
 * @file
 * Sequential API External module
 *
 * @defgroup netconn Netconn API
 * @ingroup sequential_api
 * Thread-safe, to be called from non-TCPIP threads only.
 * TX/RX handling based on @ref netbuf (containing @ref pbuf)
 * to avoid copying data around.
 *
 * @defgroup netconn_common Common functions
 * @ingroup netconn
 * For use with TCP and UDP
 *
 * @defgroup netconn_tcp TCP only
 * @ingroup netconn
 * TCP only functions
 *
 * @defgroup netconn_udp UDP only
 * @ingroup netconn
 * UDP only functions
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 */

/* This is the part of the API that is linked with
   the application */

#include "lwip/opt.h"

#if LWIP_NETCONN /* don't build if not configured for use in lwipopts.h */

#include "lwip/api.h"
#include "lwip/memp.h"

#include "lwip/ip.h"
#include "lwip/raw.h"
#include "lwip/udp.h"
#include "lwip/priv/api_msg.h"
#include "lwip/priv/tcp_priv.h"
#include "lwip/priv/tcpip_priv.h"

#ifdef LWIP_HOOK_FILENAME
#include LWIP_HOOK_FILENAME
#endif

#include <string.h>

#define API_MSG_VAR_REF(name) API_VAR_REF(name)
#define API_MSG_VAR_DECLARE(name) API_VAR_DECLARE(struct api_msg, name)
#define API_MSG_VAR_ALLOC(name)                                                \
    API_VAR_ALLOC(struct api_msg, MEMP_API_MSG, name, ERR_MEM)
#define API_MSG_VAR_ALLOC_RETURN_NULL(name)                                    \
    API_VAR_ALLOC(struct api_msg, MEMP_API_MSG, name, NULL)
#define API_MSG_VAR_FREE(name) API_VAR_FREE(MEMP_API_MSG, name)

#if TCP_LISTEN_BACKLOG
/* need to allocate API message for accept so empty message pool does not result
 * in event loss see bug #47512: MPU_COMPATIBLE may fail on empty pool */
#define API_MSG_VAR_ALLOC_ACCEPT(msg) API_MSG_VAR_ALLOC(msg)
#define API_MSG_VAR_FREE_ACCEPT(msg) API_MSG_VAR_FREE(msg)
#else /* TCP_LISTEN_BACKLOG */
#define API_MSG_VAR_ALLOC_ACCEPT(msg)
#define API_MSG_VAR_FREE_ACCEPT(msg)
#endif /* TCP_LISTEN_BACKLOG */

#if LWIP_NETCONN_FULLDUPLEX
#define NETCONN_RECVMBOX_WAITABLE(conn)                                        \
    (sys_mbox_valid(&(conn)->recvmbox) &&                                      \
     (((conn)->flags & NETCONN_FLAG_MBOXINVALID) == 0))
#define NETCONN_ACCEPTMBOX_WAITABLE(conn)                                      \
    (sys_mbox_valid(&(conn)->acceptmbox) &&                                    \
     (((conn)->flags &                                                         \
       (NETCONN_FLAG_MBOXCLOSED | NETCONN_FLAG_MBOXINVALID)) == 0))
#define NETCONN_MBOX_WAITING_INC(conn)                                         \
    SYS_ARCH_INC(conn->mbox_threads_waiting, 1)
#define NETCONN_MBOX_WAITING_DEC(conn)                                         \
    SYS_ARCH_DEC(conn->mbox_threads_waiting, 1)
#else /* LWIP_NETCONN_FULLDUPLEX */
#define NETCONN_RECVMBOX_WAITABLE(conn) sys_mbox_valid(&(conn)->recvmbox)
#define NETCONN_ACCEPTMBOX_WAITABLE(conn)                                      \
    (sys_mbox_valid(&(conn)->acceptmbox) &&                                    \
     (((conn)->flags & NETCONN_FLAG_MBOXCLOSED) == 0))
#define NETCONN_MBOX_WAITING_INC(conn)
#define NETCONN_MBOX_WAITING_DEC(conn)
#endif /* LWIP_NETCONN_FULLDUPLEX */

static err_t netconn_close_shutdown(struct netconn *conn, u8_t how);

/**
 * Call the lower part of a netconn_* function
 * This function is then running in the thread context
 * of tcpip_thread and has exclusive access to lwIP core code.
 *
 * @param fn function to call
 * @param apimsg a struct containing the function to call and its parameters
 * @return ERR_OK if the function was called, another err_t if not
 */
static err_t netconn_apimsg(tcpip_callback_fn fn, struct api_msg *apimsg) {
    err_t err;

#ifdef LWIP_DEBUG
    /* catch functions that don't set err */
    apimsg->err = ERR_VAL;
#endif /* LWIP_DEBUG */

#if LWIP_NETCONN_SEM_PER_THREAD
    apimsg->op_completed_sem = LWIP_NETCONN_THREAD_SEM_GET();
#endif /* LWIP_NETCONN_SEM_PER_THREAD */

    err = tcpip_send_msg_wait_sem(fn, apimsg, LWIP_API_MSG_SEM(apimsg));
    if (err == ERR_OK) {
        return apimsg->err;
    }
    return err;
}

/**
 * Create a new netconn (of a specific type) that has a callback function.
 * The corresponding pcb is also created.
 *
 * @param t the type of 'connection' to create (@see enum netconn_type)
 * @param proto the IP protocol for RAW IP pcbs
 * @param callback a function to call on status changes (RX available, TX'ed)
 * @return a newly allocated struct netconn or
 *         NULL on memory error
 */
struct netconn *netconn_new_with_proto_and_callback(enum netconn_type t,
                                                    u8_t proto,
                                                    netconn_callback callback) {
    struct netconn *conn;
    API_MSG_VAR_DECLARE(msg);
    API_MSG_VAR_ALLOC_RETURN_NULL(msg);

    conn = netconn_alloc(t, callback);
    if (conn != NULL) {
        err_t err;

        API_MSG_VAR_REF(msg).msg.n.proto = proto;
        API_MSG_VAR_REF(msg).conn = conn;
        err = netconn_apimsg(lwip_netconn_do_newconn, &API_MSG_VAR_REF(msg));
        if (err != ERR_OK) {
            LWIP_ASSERT("freeing conn without freeing pcb",
                        conn->pcb.tcp == NULL);
            LWIP_ASSERT("conn has no recvmbox",
                        sys_mbox_valid(&conn->recvmbox));
#if LWIP_TCP
            LWIP_ASSERT("conn->acceptmbox shouldn't exist",
                        !sys_mbox_valid(&conn->acceptmbox));
#endif /* LWIP_TCP */
#if !LWIP_NETCONN_SEM_PER_THREAD
            LWIP_ASSERT("conn has no op_completed",
                        sys_sem_valid(&conn->op_completed));
            sys_sem_free(&conn->op_completed);
#endif /* !LWIP_NETCONN_SEM_PER_THREAD */
            sys_mbox_free(&conn->recvmbox);
            memp_free(MEMP_NETCONN, conn);
            API_MSG_VAR_FREE(msg);
            return NULL;
        }
    }
    API_MSG_VAR_FREE(msg);
    return conn;
}

/**
 * @ingroup netconn_common
 * Close a netconn 'connection' and free all its resources but not the netconn
 * itself. UDP and RAW connection are completely closed, TCP pcbs might still be
 * in a waitstate after this returns.
 *
 * @param conn the netconn to delete
 * @return ERR_OK if the connection was deleted
 */
err_t netconn_prepare_delete(struct netconn *conn) {
    err_t err;
    API_MSG_VAR_DECLARE(msg);

    /* No ASSERT here because possible to get a (conn == NULL) if we got an
     * accept error */
    if (conn == NULL) {
        return ERR_OK;
    }

    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
#if LWIP_TCP
#if LWIP_SO_SNDTIMEO || LWIP_SO_LINGER
    /* get the time we started, which is later compared to
       sys_now() + conn->send_timeout */
    API_MSG_VAR_REF(msg).msg.sd.time_started = sys_now();
#else  /* LWIP_SO_SNDTIMEO || LWIP_SO_LINGER */
    API_MSG_VAR_REF(msg).msg.sd.polls_left =
        ((LWIP_TCP_CLOSE_TIMEOUT_MS_DEFAULT + TCP_SLOW_INTERVAL - 1) /
         TCP_SLOW_INTERVAL) +
        1;
#endif /* LWIP_SO_SNDTIMEO || LWIP_SO_LINGER */
#endif /* LWIP_TCP */
    err = netconn_apimsg(lwip_netconn_do_delconn, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    if (err != ERR_OK) {
        return err;
    }
    return ERR_OK;
}

/**
 * @ingroup netconn_common
 * Close a netconn 'connection' and free its resources.
 * UDP and RAW connection are completely closed, TCP pcbs might still be in a
 * waitstate after this returns.
 *
 * @param conn the netconn to delete
 * @return ERR_OK if the connection was deleted
 */
err_t netconn_delete(struct netconn *conn) {
    err_t err;

    /* No ASSERT here because possible to get a (conn == NULL) if we got an
     * accept error */
    if (conn == NULL) {
        return ERR_OK;
    }

#if LWIP_NETCONN_FULLDUPLEX
    if (conn->flags & NETCONN_FLAG_MBOXINVALID) {
        /* Already called netconn_prepare_delete() before */
        err = ERR_OK;
    } else
#endif /* LWIP_NETCONN_FULLDUPLEX */
    {
        err = netconn_prepare_delete(conn);
    }
    if (err == ERR_OK) {
        netconn_free(conn);
    }
    return err;
}

/**
 * Get the local or remote IP address and port of a netconn.
 * For RAW netconns, this returns the protocol instead of a port!
 *
 * @param conn the netconn to query
 * @param addr a pointer to which to save the IP address
 * @param port a pointer to which to save the port (or protocol for RAW)
 * @param local 1 to get the local IP address, 0 to get the remote one
 * @return ERR_CONN for invalid connections
 *         ERR_OK if the information was retrieved
 */
err_t netconn_getaddr(struct netconn *conn, ip_addr_t *addr, u16_t *port,
                      u8_t local) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;

    LWIP_ERROR("netconn_getaddr: invalid conn", (conn != NULL),
               return ERR_ARG;);
    LWIP_ERROR("netconn_getaddr: invalid addr", (addr != NULL),
               return ERR_ARG;);
    LWIP_ERROR("netconn_getaddr: invalid port", (port != NULL),
               return ERR_ARG;);

    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.ad.local = local;
#if LWIP_MPU_COMPATIBLE
    err = netconn_apimsg(lwip_netconn_do_getaddr, &API_MSG_VAR_REF(msg));
    *addr = msg->msg.ad.ipaddr;
    *port = msg->msg.ad.port;
#else  /* LWIP_MPU_COMPATIBLE */
    msg.msg.ad.ipaddr = addr;
    msg.msg.ad.port = port;
    err = netconn_apimsg(lwip_netconn_do_getaddr, &msg);
#endif /* LWIP_MPU_COMPATIBLE */
    API_MSG_VAR_FREE(msg);

    return err;
}

/**
 * @ingroup netconn_common
 * Bind a netconn to a specific local IP address and port.
 * Binding one netconn twice might not always be checked correctly!
 *
 * @param conn the netconn to bind
 * @param addr the local IP address to bind the netconn to
 *             (use IP4_ADDR_ANY/IP6_ADDR_ANY to bind to all addresses)
 * @param port the local port to bind the netconn to (not used for RAW)
 * @return ERR_OK if bound, any other err_t on failure
 */
err_t netconn_bind(struct netconn *conn, const ip_addr_t *addr, u16_t port) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;

    LWIP_ERROR("netconn_bind: invalid conn", (conn != NULL), return ERR_ARG;);

#if LWIP_IPV4
    /* Don't propagate NULL pointer (IP_ADDR_ANY alias) to subsequent functions
     */
    if (addr == NULL) {
        addr = IP4_ADDR_ANY;
    }
#endif /* LWIP_IPV4 */

#if LWIP_IPV4 && LWIP_IPV6
    /* "Socket API like" dual-stack support: If IP to bind to is IP6_ADDR_ANY,
     * and NETCONN_FLAG_IPV6_V6ONLY is 0, use IP_ANY_TYPE to bind
     */
    if ((netconn_get_ipv6only(conn) == 0) && ip_addr_eq(addr, IP6_ADDR_ANY)) {
        addr = IP_ANY_TYPE;
    }
#endif /* LWIP_IPV4 && LWIP_IPV6 */

    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.bc.ipaddr = API_MSG_VAR_REF(addr);
    API_MSG_VAR_REF(msg).msg.bc.port = port;
    err = netconn_apimsg(lwip_netconn_do_bind, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    return err;
}

/**
 * @ingroup netconn_common
 * Bind a netconn to a specific interface and port.
 * Binding one netconn twice might not always be checked correctly!
 *
 * @param conn the netconn to bind
 * @param if_idx the local interface index to bind the netconn to
 * @return ERR_OK if bound, any other err_t on failure
 */
err_t netconn_bind_if(struct netconn *conn, u8_t if_idx) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;

    LWIP_ERROR("netconn_bind_if: invalid conn", (conn != NULL),
               return ERR_ARG;);

    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.bc.if_idx = if_idx;
    err = netconn_apimsg(lwip_netconn_do_bind_if, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    return err;
}

/**
 * @ingroup netconn_common
 * Connect a netconn to a specific remote IP address and port.
 *
 * @param conn the netconn to connect
 * @param addr the remote IP address to connect to
 * @param port the remote port to connect to (no used for RAW)
 * @return ERR_OK if connected, return value of tcp_/udp_/raw_connect otherwise
 */
err_t netconn_connect(struct netconn *conn, const ip_addr_t *addr, u16_t port) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;

    LWIP_ERROR("netconn_connect: invalid conn", (conn != NULL),
               return ERR_ARG;);

#if LWIP_IPV4
    /* Don't propagate NULL pointer (IP_ADDR_ANY alias) to subsequent functions
     */
    if (addr == NULL) {
        addr = IP4_ADDR_ANY;
    }
#endif /* LWIP_IPV4 */

    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.bc.ipaddr = API_MSG_VAR_REF(addr);
    API_MSG_VAR_REF(msg).msg.bc.port = port;
    err = netconn_apimsg(lwip_netconn_do_connect, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    return err;
}

/**
 * @ingroup netconn_udp
 * Disconnect a netconn from its current peer (only valid for UDP netconns).
 *
 * @param conn the netconn to disconnect
 * @return See @ref err_t
 */
err_t netconn_disconnect(struct netconn *conn) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;

    LWIP_ERROR("netconn_disconnect: invalid conn", (conn != NULL),
               return ERR_ARG;);

    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    err = netconn_apimsg(lwip_netconn_do_disconnect, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    return err;
}

/**
 * @ingroup netconn_tcp
 * Set a TCP netconn into listen mode
 *
 * @param conn the tcp netconn to set to listen mode
 * @param backlog the listen backlog, only used if TCP_LISTEN_BACKLOG==1
 * @return ERR_OK if the netconn was set to listen (UDP and RAW netconns
 *         don't return any error (yet?))
 */
err_t netconn_listen_with_backlog(struct netconn *conn, u8_t backlog) {
#if LWIP_TCP
    API_MSG_VAR_DECLARE(msg);
    err_t err;

    /* This does no harm. If TCP_LISTEN_BACKLOG is off, backlog is unused. */
    LWIP_UNUSED_ARG(backlog);

    LWIP_ERROR("netconn_listen: invalid conn", (conn != NULL), return ERR_ARG;);

    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
#if TCP_LISTEN_BACKLOG
    API_MSG_VAR_REF(msg).msg.lb.backlog = backlog;
#endif /* TCP_LISTEN_BACKLOG */
    err = netconn_apimsg(lwip_netconn_do_listen, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    return err;
#else  /* LWIP_TCP */
    LWIP_UNUSED_ARG(conn);
    LWIP_UNUSED_ARG(backlog);
    return ERR_ARG;
#endif /* LWIP_TCP */
}

/**
 * @ingroup netconn_tcp
 * Accept a new connection on a TCP listening netconn.
 *
 * @param conn the TCP listen netconn
 * @param new_conn pointer where the new connection is stored
 * @return ERR_OK if a new connection has been received or an error
 *                code otherwise
 */
err_t netconn_accept(struct netconn *conn, struct netconn **new_conn) {
#if LWIP_TCP
    err_t err;
    void *accept_ptr;
    struct netconn *newconn;
#if TCP_LISTEN_BACKLOG
    API_MSG_VAR_DECLARE(msg);
#endif /* TCP_LISTEN_BACKLOG */

    LWIP_ERROR("netconn_accept: invalid pointer", (new_conn != NULL),
               return ERR_ARG;);
    *new_conn = NULL;
    LWIP_ERROR("netconn_accept: invalid conn", (conn != NULL), return ERR_ARG;);

    /* NOTE: Although the opengroup spec says a pending error shall be returned
       to send/recv/getsockopt(SO_ERROR) only, we return it for listening
             connections also, to handle embedded-system errors */
    err = netconn_err(conn);
    if (err != ERR_OK) {
        /* return pending error */
        return err;
    }
    if (!NETCONN_ACCEPTMBOX_WAITABLE(conn)) {
        /* don't accept if closed: this might block the application task
           waiting on acceptmbox forever! */
        return ERR_CLSD;
    }

    API_MSG_VAR_ALLOC_ACCEPT(msg);

    NETCONN_MBOX_WAITING_INC(conn);
    if (netconn_is_nonblocking(conn)) {
        if (sys_arch_mbox_tryfetch(&conn->acceptmbox, &accept_ptr) ==
            SYS_MBOX_EMPTY) {
            API_MSG_VAR_FREE_ACCEPT(msg);
            NETCONN_MBOX_WAITING_DEC(conn);
            return ERR_WOULDBLOCK;
        }
    } else {
#if LWIP_SO_RCVTIMEO
        if (sys_arch_mbox_fetch(&conn->acceptmbox, &accept_ptr,
                                conn->recv_timeout) == SYS_ARCH_TIMEOUT) {
            API_MSG_VAR_FREE_ACCEPT(msg);
            NETCONN_MBOX_WAITING_DEC(conn);
            return ERR_TIMEOUT;
        }
#else
        sys_arch_mbox_fetch(&conn->acceptmbox, &accept_ptr, 0);
#endif /* LWIP_SO_RCVTIMEO*/
    }
    NETCONN_MBOX_WAITING_DEC(conn);
#if LWIP_NETCONN_FULLDUPLEX
    if (conn->flags & NETCONN_FLAG_MBOXINVALID) {
        if (lwip_netconn_is_deallocated_msg(accept_ptr)) {
            /* the netconn has been closed from another thread */
            API_MSG_VAR_FREE_ACCEPT(msg);
            return ERR_CONN;
        }
    }
#endif

    /* Register event with callback */
    API_EVENT(conn, NETCONN_EVT_RCVMINUS, 0);

    if (lwip_netconn_is_err_msg(accept_ptr, &err)) {
        /* a connection has been aborted: e.g. out of pcbs or out of netconns
         * during accept */
        API_MSG_VAR_FREE_ACCEPT(msg);
        return err;
    }
    if (accept_ptr == NULL) {
        /* connection has been aborted */
        API_MSG_VAR_FREE_ACCEPT(msg);
        return ERR_CLSD;
    }
    newconn = (struct netconn *)accept_ptr;
#if TCP_LISTEN_BACKLOG
    /* Let the stack know that we have accepted the connection. */
    API_MSG_VAR_REF(msg).conn = newconn;
    /* don't care for the return value of lwip_netconn_do_recv */
    netconn_apimsg(lwip_netconn_do_accepted, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
#endif /* TCP_LISTEN_BACKLOG */

    *new_conn = newconn;
    /* don't set conn->last_err: it's only ERR_OK, anyway */
    return ERR_OK;
#else  /* LWIP_TCP */
    LWIP_UNUSED_ARG(conn);
    LWIP_UNUSED_ARG(new_conn);
    return ERR_ARG;
#endif /* LWIP_TCP */
}

/**
 * @ingroup netconn_common
 * Receive data: actual implementation that doesn't care whether pbuf or netbuf
 * is received (this is internal, it's just here for describing common errors)
 *
 * @param conn the netconn from which to receive data
 * @param new_buf pointer where a new pbuf/netbuf is stored when received data
 * @param apiflags flags that control function behaviour. For now only:
 * - NETCONN_DONTBLOCK: only read data that is available now, don't wait for
 * more data
 * @return ERR_OK if data has been received, an error code otherwise (timeout,
 *                memory error or another error)
 *         ERR_CONN if not connected
 *         ERR_CLSD if TCP connection has been closed
 *         ERR_WOULDBLOCK if the netconn is nonblocking but would block to wait
 * for data ERR_TIMEOUT if the netconn has a receive timeout and no data was
 * received
 */
static err_t netconn_recv_data(struct netconn *conn, void **new_buf,
                               u8_t apiflags) {
    void *buf = NULL;
    u16_t len;

    LWIP_ERROR("netconn_recv: invalid pointer", (new_buf != NULL),
               return ERR_ARG;);
    *new_buf = NULL;
    LWIP_ERROR("netconn_recv: invalid conn", (conn != NULL), return ERR_ARG;);

    if (!NETCONN_RECVMBOX_WAITABLE(conn)) {
        err_t err = netconn_err(conn);
        if (err != ERR_OK) {
            /* return pending error */
            return err;
        }
        return ERR_CONN;
    }

    NETCONN_MBOX_WAITING_INC(conn);
    if (netconn_is_nonblocking(conn) || (apiflags & NETCONN_DONTBLOCK) ||
        (conn->flags & NETCONN_FLAG_MBOXCLOSED) ||
        (conn->pending_err != ERR_OK)) {
        if (sys_arch_mbox_tryfetch(&conn->recvmbox, &buf) == SYS_MBOX_EMPTY) {
            err_t err;
            NETCONN_MBOX_WAITING_DEC(conn);
            err = netconn_err(conn);
            if (err != ERR_OK) {
                /* return pending error */
                return err;
            }
            if (conn->flags & NETCONN_FLAG_MBOXCLOSED) {
                return ERR_CONN;
            }
            return ERR_WOULDBLOCK;
        }
    } else {
#if LWIP_SO_RCVTIMEO
        if (sys_arch_mbox_fetch(&conn->recvmbox, &buf, conn->recv_timeout) ==
            SYS_ARCH_TIMEOUT) {
            NETCONN_MBOX_WAITING_DEC(conn);
            return ERR_TIMEOUT;
        }
#else
        sys_arch_mbox_fetch(&conn->recvmbox, &buf, 0);
#endif /* LWIP_SO_RCVTIMEO*/
    }
    NETCONN_MBOX_WAITING_DEC(conn);
#if LWIP_NETCONN_FULLDUPLEX
    if (conn->flags & NETCONN_FLAG_MBOXINVALID) {
        if (lwip_netconn_is_deallocated_msg(buf)) {
            /* the netconn has been closed from another thread */
            API_MSG_VAR_FREE_ACCEPT(msg);
            return ERR_CONN;
        }
    }
#endif

#if LWIP_TCP
#if (LWIP_UDP || LWIP_RAW)
    if (NETCONNTYPE_GROUP(conn->type) == NETCONN_TCP)
#endif /* (LWIP_UDP || LWIP_RAW) */
    {
        err_t err;
        /* Check if this is an error message or a pbuf */
        if (lwip_netconn_is_err_msg(buf, &err)) {
            /* new_buf has been zeroed above already */
            if (err == ERR_CLSD) {
                /* connection closed translates to ERR_OK with *new_buf == NULL
                 */
                return ERR_OK;
            }
            return err;
        }
        len = ((struct pbuf *)buf)->tot_len;
    }
#endif /* LWIP_TCP */
#if LWIP_TCP && (LWIP_UDP || LWIP_RAW)
    else
#endif /* LWIP_TCP && (LWIP_UDP || LWIP_RAW) */
#if (LWIP_UDP || LWIP_RAW)
    {
        LWIP_ASSERT("buf != NULL", buf != NULL);
        len = netbuf_len((struct netbuf *)buf);
    }
#endif /* (LWIP_UDP || LWIP_RAW) */

#if LWIP_SO_RCVBUF
    SYS_ARCH_DEC(conn->recv_avail, len);
#endif /* LWIP_SO_RCVBUF */
    /* Register event with callback */
    API_EVENT(conn, NETCONN_EVT_RCVMINUS, len);

    LWIP_DEBUGF(API_LIB_DEBUG,
                ("netconn_recv_data: received %p, len=%" U16_F "\n", buf, len));

    *new_buf = buf;
    /* don't set conn->last_err: it's only ERR_OK, anyway */
    return ERR_OK;
}

#if LWIP_TCP
static err_t netconn_tcp_recvd_msg(struct netconn *conn, size_t len,
                                   struct api_msg *msg) {
    LWIP_ERROR("netconn_recv_tcp_pbuf: invalid conn",
               (conn != NULL) &&
                   NETCONNTYPE_GROUP(netconn_type(conn)) == NETCONN_TCP,
               return ERR_ARG;);

    msg->conn = conn;
    msg->msg.r.len = len;

    return netconn_apimsg(lwip_netconn_do_recv, msg);
}

err_t netconn_tcp_recvd(struct netconn *conn, size_t len) {
    err_t err;
    API_MSG_VAR_DECLARE(msg);
    LWIP_ERROR("netconn_recv_tcp_pbuf: invalid conn",
               (conn != NULL) &&
                   NETCONNTYPE_GROUP(netconn_type(conn)) == NETCONN_TCP,
               return ERR_ARG;);

    API_MSG_VAR_ALLOC(msg);
    err = netconn_tcp_recvd_msg(conn, len, &API_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);
    return err;
}

static err_t netconn_recv_data_tcp(struct netconn *conn, struct pbuf **new_buf,
                                   u8_t apiflags) {
    err_t err;
    struct pbuf *buf;
    API_MSG_VAR_DECLARE(msg);
#if LWIP_MPU_COMPATIBLE
    msg = NULL;
#endif

    if (!NETCONN_RECVMBOX_WAITABLE(conn)) {
        /* This only happens when calling this function more than once *after*
         * receiving FIN */
        return ERR_CONN;
    }
    if (netconn_is_flag_set(conn, NETCONN_FIN_RX_PENDING)) {
        netconn_clear_flags(conn, NETCONN_FIN_RX_PENDING);
        goto handle_fin;
    }

    if (!(apiflags & NETCONN_NOAUTORCVD)) {
        /* need to allocate API message here so empty message pool does not
         * result in event loss see bug #47512: MPU_COMPATIBLE may fail on empty
         * pool */
        API_MSG_VAR_ALLOC(msg);
    }

    err = netconn_recv_data(conn, (void **)new_buf, apiflags);
    if (err != ERR_OK) {
        if (!(apiflags & NETCONN_NOAUTORCVD)) {
            API_MSG_VAR_FREE(msg);
        }
        return err;
    }
    buf = *new_buf;
    if (!(apiflags & NETCONN_NOAUTORCVD)) {
        /* Let the stack know that we have taken the data. */
        u16_t len = buf ? buf->tot_len : 1;
        /* don't care for the return value of lwip_netconn_do_recv */
        /* @todo: this should really be fixed, e.g. by retrying in poll on error
         */
        netconn_tcp_recvd_msg(conn, len, &API_VAR_REF(msg));
        API_MSG_VAR_FREE(msg);
    }

    /* If we are closed, we indicate that we no longer wish to use the socket */
    if (buf == NULL) {
        if (apiflags & NETCONN_NOFIN) {
            /* received a FIN but the caller cannot handle it right now:
               re-enqueue it and return "no data" */
            netconn_set_flags(conn, NETCONN_FIN_RX_PENDING);
            return ERR_WOULDBLOCK;
        } else {
        handle_fin:
            API_EVENT(conn, NETCONN_EVT_RCVMINUS, 0);
            if (conn->pcb.ip == NULL) {
                /* race condition: RST during recv */
                err = netconn_err(conn);
                if (err != ERR_OK) {
                    return err;
                }
                return ERR_RST;
            }
            /* RX side is closed, so deallocate the recvmbox */
            netconn_close_shutdown(conn, NETCONN_SHUT_RD);
            /* Don' store ERR_CLSD as conn->err since we are only half-closed */
            return ERR_CLSD;
        }
    }
    return err;
}

/**
 * @ingroup netconn_tcp
 * Receive data (in form of a pbuf) from a TCP netconn
 *
 * @param conn the netconn from which to receive data
 * @param new_buf pointer where a new pbuf is stored when received data
 * @return ERR_OK if data has been received, an error code otherwise (timeout,
 *                memory error or another error, @see netconn_recv_data)
 *         ERR_ARG if conn is not a TCP netconn
 */
err_t netconn_recv_tcp_pbuf(struct netconn *conn, struct pbuf **new_buf) {
    LWIP_ERROR("netconn_recv_tcp_pbuf: invalid conn",
               (conn != NULL) &&
                   NETCONNTYPE_GROUP(netconn_type(conn)) == NETCONN_TCP,
               return ERR_ARG;);

    return netconn_recv_data_tcp(conn, new_buf, 0);
}

/**
 * @ingroup netconn_tcp
 * Receive data (in form of a pbuf) from a TCP netconn
 *
 * @param conn the netconn from which to receive data
 * @param new_buf pointer where a new pbuf is stored when received data
 * @param apiflags flags that control function behaviour. For now only:
 * - NETCONN_DONTBLOCK: only read data that is available now, don't wait for
 * more data
 * @return ERR_OK if data has been received, an error code otherwise (timeout,
 *                memory error or another error, @see netconn_recv_data)
 *         ERR_ARG if conn is not a TCP netconn
 */
err_t netconn_recv_tcp_pbuf_flags(struct netconn *conn, struct pbuf **new_buf,
                                  u8_t apiflags) {
    LWIP_ERROR("netconn_recv_tcp_pbuf: invalid conn",
               (conn != NULL) &&
                   NETCONNTYPE_GROUP(netconn_type(conn)) == NETCONN_TCP,
               return ERR_ARG;);

    return netconn_recv_data_tcp(conn, new_buf, apiflags);
}
#endif /* LWIP_TCP */

/**
 * Receive data (in form of a netbuf) from a UDP or RAW netconn
 *
 * @param conn the netconn from which to receive data
 * @param new_buf pointer where a new netbuf is stored when received data
 * @return ERR_OK if data has been received, an error code otherwise (timeout,
 *                memory error or another error)
 *         ERR_ARG if conn is not a UDP/RAW netconn
 */
err_t netconn_recv_udp_raw_netbuf(struct netconn *conn,
                                  struct netbuf **new_buf) {
    LWIP_ERROR("netconn_recv_udp_raw_netbuf: invalid conn",
               (conn != NULL) &&
                   NETCONNTYPE_GROUP(netconn_type(conn)) != NETCONN_TCP,
               return ERR_ARG;);

    return netconn_recv_data(conn, (void **)new_buf, 0);
}

/**
 * Receive data (in form of a netbuf) from a UDP or RAW netconn
 *
 * @param conn the netconn from which to receive data
 * @param new_buf pointer where a new netbuf is stored when received data
 * @param apiflags flags that control function behaviour. For now only:
 * - NETCONN_DONTBLOCK: only read data that is available now, don't wait for
 * more data
 * @return ERR_OK if data has been received, an error code otherwise (timeout,
 *                memory error or another error)
 *         ERR_ARG if conn is not a UDP/RAW netconn
 */
err_t netconn_recv_udp_raw_netbuf_flags(struct netconn *conn,
                                        struct netbuf **new_buf,
                                        u8_t apiflags) {
    LWIP_ERROR("netconn_recv_udp_raw_netbuf: invalid conn",
               (conn != NULL) &&
                   NETCONNTYPE_GROUP(netconn_type(conn)) != NETCONN_TCP,
               return ERR_ARG;);

    return netconn_recv_data(conn, (void **)new_buf, apiflags);
}

/**
 * @ingroup netconn_common
 * Receive data (in form of a netbuf containing a packet buffer) from a netconn
 *
 * @param conn the netconn from which to receive data
 * @param new_buf pointer where a new netbuf is stored when received data
 * @return ERR_OK if data has been received, an error code otherwise (timeout,
 *                memory error or another error)
 */
err_t netconn_recv(struct netconn *conn, struct netbuf **new_buf) {
#if LWIP_TCP
    struct netbuf *buf = NULL;
    err_t err;
#endif /* LWIP_TCP */

    LWIP_ERROR("netconn_recv: invalid pointer", (new_buf != NULL),
               return ERR_ARG;);
    *new_buf = NULL;
    LWIP_ERROR("netconn_recv: invalid conn", (conn != NULL), return ERR_ARG;);

#if LWIP_TCP
#if (LWIP_UDP || LWIP_RAW)
    if (NETCONNTYPE_GROUP(conn->type) == NETCONN_TCP)
#endif /* (LWIP_UDP || LWIP_RAW) */
    {
        struct pbuf *p = NULL;
        /* This is not a listening netconn, since recvmbox is set */

        buf = (struct netbuf *)memp_malloc(MEMP_NETBUF);
        if (buf == NULL) {
            return ERR_MEM;
        }

        err = netconn_recv_data_tcp(conn, &p, 0);
        if (err != ERR_OK) {
            memp_free(MEMP_NETBUF, buf);
            return err;
        }
        LWIP_ASSERT("p != NULL", p != NULL);

        buf->p = p;
        buf->ptr = p;
        buf->port = 0;
        ip_addr_set_zero(&buf->addr);
        *new_buf = buf;
        /* don't set conn->last_err: it's only ERR_OK, anyway */
        return ERR_OK;
    }
#endif /* LWIP_TCP */
#if LWIP_TCP && (LWIP_UDP || LWIP_RAW)
    else
#endif /* LWIP_TCP && (LWIP_UDP || LWIP_RAW) */
    {
#if (LWIP_UDP || LWIP_RAW)
        return netconn_recv_data(conn, (void **)new_buf, 0);
#endif /* (LWIP_UDP || LWIP_RAW) */
    }
}

/**
 * @ingroup netconn_udp
 * Send data (in form of a netbuf) to a specific remote IP address and port.
 * Only to be used for UDP and RAW netconns (not TCP).
 *
 * @param conn the netconn over which to send data
 * @param buf a netbuf containing the data to send
 * @param addr the remote IP address to which to send the data
 * @param port the remote port to which to send the data
 * @return ERR_OK if data was sent, any other err_t on error
 */
err_t netconn_sendto(struct netconn *conn, struct netbuf *buf,
                     const ip_addr_t *addr, u16_t port) {
    if (buf != NULL) {
        ip_addr_set(&buf->addr, addr);
        buf->port = port;
        return netconn_send(conn, buf);
    }
    return ERR_VAL;
}

/**
 * @ingroup netconn_udp
 * Send data over a UDP or RAW netconn (that is already connected).
 *
 * @param conn the UDP or RAW netconn over which to send data
 * @param buf a netbuf containing the data to send
 * @return ERR_OK if data was sent, any other err_t on error
 */
err_t netconn_send(struct netconn *conn, struct netbuf *buf) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;

    LWIP_ERROR("netconn_send: invalid conn", (conn != NULL), return ERR_ARG;);

    LWIP_DEBUGF(API_LIB_DEBUG,
                ("netconn_send: sending %" U16_F " bytes\n", buf->p->tot_len));

    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.b = buf;
    err = netconn_apimsg(lwip_netconn_do_send, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    return err;
}

/**
 * @ingroup netconn_tcp
 * Send data over a TCP netconn.
 *
 * @param conn the TCP netconn over which to send data
 * @param dataptr pointer to the application buffer that contains the data to
 * send
 * @param size size of the application data to send
 * @param apiflags combination of following flags :
 * - NETCONN_COPY: data will be copied into memory belonging to the stack
 * - NETCONN_MORE: for TCP connection, PSH flag will be set on last segment sent
 * - NETCONN_DONTBLOCK: only write the data if all data can be written at once
 * @param bytes_written pointer to a location that receives the number of
 * written bytes
 * @return ERR_OK if data was sent, any other err_t on error
 */
err_t netconn_write_partly(struct netconn *conn, const void *dataptr,
                           size_t size, u8_t apiflags, size_t *bytes_written) {
    struct netvector vector;
    vector.ptr = dataptr;
    vector.len = size;
    return netconn_write_vectors_partly(conn, &vector, 1, apiflags,
                                        bytes_written);
}

/**
 * Send vectorized data atomically over a TCP netconn.
 *
 * @param conn the TCP netconn over which to send data
 * @param vectors array of vectors containing data to send
 * @param vectorcnt number of vectors in the array
 * @param apiflags combination of following flags :
 * - NETCONN_COPY: data will be copied into memory belonging to the stack
 * - NETCONN_MORE: for TCP connection, PSH flag will be set on last segment sent
 * - NETCONN_DONTBLOCK: only write the data if all data can be written at once
 * @param bytes_written pointer to a location that receives the number of
 * written bytes
 * @return ERR_OK if data was sent, any other err_t on error
 */
err_t netconn_write_vectors_partly(struct netconn *conn,
                                   struct netvector *vectors, u16_t vectorcnt,
                                   u8_t apiflags, size_t *bytes_written) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
    u8_t dontblock;
    size_t size;
    int i;

    LWIP_ERROR("netconn_write: invalid conn", (conn != NULL), return ERR_ARG;);
    LWIP_ERROR("netconn_write: invalid conn->type",
               (NETCONNTYPE_GROUP(conn->type) == NETCONN_TCP), return ERR_VAL;);
    dontblock = netconn_is_nonblocking(conn) || (apiflags & NETCONN_DONTBLOCK);
#if LWIP_SO_SNDTIMEO
    if (conn->send_timeout != 0) {
        dontblock = 1;
    }
#endif /* LWIP_SO_SNDTIMEO */
    if (dontblock && !bytes_written) {
        /* This implies netconn_write() cannot be used for non-blocking send,
           since it has no way to return the number of bytes written. */
        return ERR_VAL;
    }

    /* sum up the total size */
    size = 0;
    for (i = 0; i < vectorcnt; i++) {
        size += vectors[i].len;
        if (size < vectors[i].len) {
            /* overflow */
            return ERR_VAL;
        }
    }
    if (size == 0) {
        return ERR_OK;
    } else if (size > SSIZE_MAX) {
        ssize_t limited;
        /* this is required by the socket layer (cannot send full size_t range)
         */
        if (!bytes_written) {
            return ERR_VAL;
        }
        /* limit the amount of data to send */
        limited = SSIZE_MAX;
        size = (size_t)limited;
    }

    API_MSG_VAR_ALLOC(msg);
    /* non-blocking write sends as much  */
    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.w.vector = vectors;
    API_MSG_VAR_REF(msg).msg.w.vector_cnt = vectorcnt;
    API_MSG_VAR_REF(msg).msg.w.vector_off = 0;
    API_MSG_VAR_REF(msg).msg.w.apiflags = apiflags;
    API_MSG_VAR_REF(msg).msg.w.len = size;
    API_MSG_VAR_REF(msg).msg.w.offset = 0;
#if LWIP_SO_SNDTIMEO
    if (conn->send_timeout != 0) {
        /* get the time we started, which is later compared to
            sys_now() + conn->send_timeout */
        API_MSG_VAR_REF(msg).msg.w.time_started = sys_now();
    } else {
        API_MSG_VAR_REF(msg).msg.w.time_started = 0;
    }
#endif /* LWIP_SO_SNDTIMEO */

    /* For locking the core: this _can_ be delayed on low memory/low send
       buffer, but if it is, this is done inside api_msg.c:do_write(), so we can
       use the non-blocking version here. */
    err = netconn_apimsg(lwip_netconn_do_write, &API_MSG_VAR_REF(msg));
    if (err == ERR_OK) {
        if (bytes_written != NULL) {
            *bytes_written = API_MSG_VAR_REF(msg).msg.w.offset;
        }
        /* for blocking, check all requested bytes were written, NOTE:
           send_timeout is treated as dontblock (see dontblock assignment above)
         */
        if (!dontblock) {
            LWIP_ASSERT("do_write failed to write all bytes",
                        API_MSG_VAR_REF(msg).msg.w.offset == size);
        }
    }
    API_MSG_VAR_FREE(msg);

    return err;
}

/**
 * @ingroup netconn_tcp
 * Close or shutdown a TCP netconn (doesn't delete it).
 *
 * @param conn the TCP netconn to close or shutdown
 * @param how fully close or only shutdown one side?
 * @return ERR_OK if the netconn was closed, any other err_t on error
 */
static err_t netconn_close_shutdown(struct netconn *conn, u8_t how) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;
    LWIP_UNUSED_ARG(how);

    LWIP_ERROR("netconn_close: invalid conn", (conn != NULL), return ERR_ARG;);

    API_MSG_VAR_ALLOC(msg);
    API_MSG_VAR_REF(msg).conn = conn;
#if LWIP_TCP
    /* shutting down both ends is the same as closing */
    API_MSG_VAR_REF(msg).msg.sd.shut = how;
#if LWIP_SO_SNDTIMEO || LWIP_SO_LINGER
    /* get the time we started, which is later compared to
       sys_now() + conn->send_timeout */
    API_MSG_VAR_REF(msg).msg.sd.time_started = sys_now();
#else  /* LWIP_SO_SNDTIMEO || LWIP_SO_LINGER */
    API_MSG_VAR_REF(msg).msg.sd.polls_left =
        ((LWIP_TCP_CLOSE_TIMEOUT_MS_DEFAULT + TCP_SLOW_INTERVAL - 1) /
         TCP_SLOW_INTERVAL) +
        1;
#endif /* LWIP_SO_SNDTIMEO || LWIP_SO_LINGER */
#endif /* LWIP_TCP */
    err = netconn_apimsg(lwip_netconn_do_close, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    return err;
}

/**
 * @ingroup netconn_tcp
 * Close a TCP netconn (doesn't delete it).
 *
 * @param conn the TCP netconn to close
 * @return ERR_OK if the netconn was closed, any other err_t on error
 */
err_t netconn_close(struct netconn *conn) {
    /* shutting down both ends is the same as closing */
    return netconn_close_shutdown(conn, NETCONN_SHUT_RDWR);
}

/**
 * @ingroup netconn_common
 * Get and reset pending error on a netconn
 *
 * @param conn the netconn to get the error from
 * @return and pending error or ERR_OK if no error was pending
 */
err_t netconn_err(struct netconn *conn) {
    err_t err;
    SYS_ARCH_DECL_PROTECT(lev);
    if (conn == NULL) {
        return ERR_OK;
    }
    SYS_ARCH_PROTECT(lev);
    err = conn->pending_err;
    conn->pending_err = ERR_OK;
    SYS_ARCH_UNPROTECT(lev);
    return err;
}

/**
 * @ingroup netconn_tcp
 * Shut down one or both sides of a TCP netconn (doesn't delete it).
 *
 * @param conn the TCP netconn to shut down
 * @param shut_rx shut down the RX side (no more read possible after this)
 * @param shut_tx shut down the TX side (no more write possible after this)
 * @return ERR_OK if the netconn was closed, any other err_t on error
 */
err_t netconn_shutdown(struct netconn *conn, u8_t shut_rx, u8_t shut_tx) {
    return netconn_close_shutdown(conn,
                                  (u8_t)((shut_rx ? NETCONN_SHUT_RD : 0) |
                                         (shut_tx ? NETCONN_SHUT_WR : 0)));
}

#if LWIP_IGMP || (LWIP_IPV6 && LWIP_IPV6_MLD)
/**
 * @ingroup netconn_udp
 * Join multicast groups for UDP netconns.
 *
 * @param conn the UDP netconn for which to change multicast addresses
 * @param multiaddr IP address of the multicast group to join or leave
 * @param netif_addr the IP address of the network interface on which to send
 *                  the igmp message
 * @param join_or_leave flag whether to send a join- or leave-message
 * @return ERR_OK if the action was taken, any err_t on error
 */
err_t netconn_join_leave_group(struct netconn *conn, const ip_addr_t *multiaddr,
                               const ip_addr_t *netif_addr,
                               enum netconn_igmp join_or_leave) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;

    LWIP_ERROR("netconn_join_leave_group: invalid conn", (conn != NULL),
               return ERR_ARG;);

    API_MSG_VAR_ALLOC(msg);

#if LWIP_IPV4
    /* Don't propagate NULL pointer (IP_ADDR_ANY alias) to subsequent functions
     */
    if (multiaddr == NULL) {
        multiaddr = IP4_ADDR_ANY;
    }
    if (netif_addr == NULL) {
        netif_addr = IP4_ADDR_ANY;
    }
#endif /* LWIP_IPV4 */

    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.jl.multiaddr = API_MSG_VAR_REF(multiaddr);
    API_MSG_VAR_REF(msg).msg.jl.netif_addr = API_MSG_VAR_REF(netif_addr);
    API_MSG_VAR_REF(msg).msg.jl.join_or_leave = join_or_leave;
    err =
        netconn_apimsg(lwip_netconn_do_join_leave_group, &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    return err;
}
/**
 * @ingroup netconn_udp
 * Join multicast groups for UDP netconns.
 *
 * @param conn the UDP netconn for which to change multicast addresses
 * @param multiaddr IP address of the multicast group to join or leave
 * @param if_idx the index of the netif
 * @param join_or_leave flag whether to send a join- or leave-message
 * @return ERR_OK if the action was taken, any err_t on error
 */
err_t netconn_join_leave_group_netif(struct netconn *conn,
                                     const ip_addr_t *multiaddr, u8_t if_idx,
                                     enum netconn_igmp join_or_leave) {
    API_MSG_VAR_DECLARE(msg);
    err_t err;

    LWIP_ERROR("netconn_join_leave_group: invalid conn", (conn != NULL),
               return ERR_ARG;);

    API_MSG_VAR_ALLOC(msg);

#if LWIP_IPV4
    /* Don't propagate NULL pointer (IP_ADDR_ANY alias) to subsequent functions
     */
    if (multiaddr == NULL) {
        multiaddr = IP4_ADDR_ANY;
    }
    if (if_idx == NETIF_NO_INDEX) {
        return ERR_IF;
    }
#endif /* LWIP_IPV4 */

    API_MSG_VAR_REF(msg).conn = conn;
    API_MSG_VAR_REF(msg).msg.jl.multiaddr = API_MSG_VAR_REF(multiaddr);
    API_MSG_VAR_REF(msg).msg.jl.if_idx = if_idx;
    API_MSG_VAR_REF(msg).msg.jl.join_or_leave = join_or_leave;
    err = netconn_apimsg(lwip_netconn_do_join_leave_group_netif,
                         &API_MSG_VAR_REF(msg));
    API_MSG_VAR_FREE(msg);

    return err;
}
#endif /* LWIP_IGMP || (LWIP_IPV6 && LWIP_IPV6_MLD) */

#if LWIP_DNS
/**
 * @ingroup netconn_common
 * Execute a DNS query, only one IP address is returned
 *
 * @param name a string representation of the DNS host name to query
 * @param addr a preallocated ip_addr_t where to store the resolved IP address
 * @return ERR_OK: resolving succeeded
 *         ERR_MEM: memory error, try again later
 *         ERR_ARG: dns client not initialized or invalid hostname
 *         ERR_VAL: dns server response was invalid
 */
#if LWIP_IPV4 && LWIP_IPV6
/** @param dns_addrtype IP address type (IPv4 / IPv6) */
err_t netconn_gethostbyname_addrtype(const char *name, ip_addr_t *addr,
                                     u8_t dns_addrtype)
#else
err_t netconn_gethostbyname(const char *name, ip_addr_t *addr)
#endif
{
    API_VAR_DECLARE(struct dns_api_msg, msg);
#if !LWIP_MPU_COMPATIBLE
    sys_sem_t sem;
#endif /* LWIP_MPU_COMPATIBLE */
    err_t err;
    err_t cberr;

    LWIP_ERROR("netconn_gethostbyname: invalid name", (name != NULL),
               return ERR_ARG;);
    LWIP_ERROR("netconn_gethostbyname: invalid addr", (addr != NULL),
               return ERR_ARG;);
#if LWIP_MPU_COMPATIBLE
    if (strlen(name) >= DNS_MAX_NAME_LENGTH) {
        return ERR_ARG;
    }
#endif

#ifdef LWIP_HOOK_NETCONN_EXTERNAL_RESOLVE
#if LWIP_IPV4 && LWIP_IPV6
    if (LWIP_HOOK_NETCONN_EXTERNAL_RESOLVE(name, addr, dns_addrtype, &err)) {
#else
    if (LWIP_HOOK_NETCONN_EXTERNAL_RESOLVE(name, addr, NETCONN_DNS_DEFAULT,
                                           &err)) {
#endif /* LWIP_IPV4 && LWIP_IPV6 */
        return err;
    }
#endif /* LWIP_HOOK_NETCONN_EXTERNAL_RESOLVE */

    API_VAR_ALLOC(struct dns_api_msg, MEMP_DNS_API_MSG, msg, ERR_MEM);
#if LWIP_MPU_COMPATIBLE
    strncpy(API_VAR_REF(msg).name, name, DNS_MAX_NAME_LENGTH - 1);
    API_VAR_REF(msg).name[DNS_MAX_NAME_LENGTH - 1] = 0;
#else  /* LWIP_MPU_COMPATIBLE */
    msg.err = &err;
    msg.sem = &sem;
    API_VAR_REF(msg).addr = API_VAR_REF(addr);
    API_VAR_REF(msg).name = name;
#endif /* LWIP_MPU_COMPATIBLE */
#if LWIP_IPV4 && LWIP_IPV6
    API_VAR_REF(msg).dns_addrtype = dns_addrtype;
#endif /* LWIP_IPV4 && LWIP_IPV6 */
#if LWIP_NETCONN_SEM_PER_THREAD
    API_VAR_REF(msg).sem = LWIP_NETCONN_THREAD_SEM_GET();
#else  /* LWIP_NETCONN_SEM_PER_THREAD*/
    err = sys_sem_new(API_EXPR_REF(API_VAR_REF(msg).sem), 0);
    if (err != ERR_OK) {
        API_VAR_FREE(MEMP_DNS_API_MSG, msg);
        return err;
    }
#endif /* LWIP_NETCONN_SEM_PER_THREAD */

    cberr = tcpip_send_msg_wait_sem(lwip_netconn_do_gethostbyname,
                                    &API_VAR_REF(msg),
                                    API_EXPR_REF(API_VAR_REF(msg).sem));
#if !LWIP_NETCONN_SEM_PER_THREAD
    sys_sem_free(API_EXPR_REF(API_VAR_REF(msg).sem));
#endif /* !LWIP_NETCONN_SEM_PER_THREAD */
    if (cberr != ERR_OK) {
        API_VAR_FREE(MEMP_DNS_API_MSG, msg);
        return cberr;
    }

#if LWIP_MPU_COMPATIBLE
    *addr = msg->addr;
    err = msg->err;
#endif /* LWIP_MPU_COMPATIBLE */

    API_VAR_FREE(MEMP_DNS_API_MSG, msg);
    return err;
}
#endif /* LWIP_DNS*/

#if LWIP_NETCONN_SEM_PER_THREAD
void netconn_thread_init(void) {
    sys_sem_t *sem = LWIP_NETCONN_THREAD_SEM_GET();
    if (!sys_sem_valid(sem)) {
        /* call alloc only once */
        LWIP_NETCONN_THREAD_SEM_ALLOC();
        LWIP_ASSERT("LWIP_NETCONN_THREAD_SEM_ALLOC() failed",
                    sys_sem_valid(LWIP_NETCONN_THREAD_SEM_GET()));
    }
}

void netconn_thread_cleanup(void) {
    sys_sem_t *sem = LWIP_NETCONN_THREAD_SEM_GET();
    if (sys_sem_valid(sem)) {
        /* call free only once */
        LWIP_NETCONN_THREAD_SEM_FREE();
    }
}
#endif /* LWIP_NETCONN_SEM_PER_THREAD */

#endif /* LWIP_NETCONN */
